Semiconductor element and display device using the same

ABSTRACT

Provided is a semiconductor element including: a semiconductor having an active layer; a gate insulating film which is in contact with the semiconductor; a gate electrode opposite to the active layer through the gate insulating film; a first nitride insulating film formed over the active layer; a photosensitive organic resin film formed on the first nitride insulating film; a second nitride insulating film formed on the photosensitive organic resin film; and a wiring provided on the second nitride insulating film, in which a first opening portion is provided in the photosensitive organic resin film, an inner wall surface of the first opening portion is covered with the second nitride insulating film, a second opening portion is provided in a laminate including the gate insulating film, the first nitride insulating film, and the second nitride insulating film inside the first opening portion, and the semiconductor is connected with the wiring through the first opening portion and the second opening portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor element (typically, atransistor) and a manufacturing method thereof, and more specificallybelongs to a technique of a display device using a thin film transistoras a device. That is, the present invention belongs to a techniqueconcerning a display device represented by a liquid crystal displaydevice, an electroluminescence display device, or the like, a techniqueconcerning a sensor represented by a CMOS sensor or the like, and othertechniques concerning various semiconductor devices in which asemiconductor integrated circuit is mounted.

2. Description of the Related Art

In recent years, the developments for a liquid crystal display deviceand an electroluminescence display device in which thin film transistors(TFTs) are integrated on a glass substrate have been progressed. Thesedisplay devices each are one of semiconductor devices characterized inthat thin film transistors are formed on glass substrate using a thinfilm formation technique and a liquid crystal element or anelectroluminescence (hereinafter referred to as just an EL) element isformed on various circuits composed of the thin film transistors, sothat a function as a display device is provided.

The circuits composed of the thin film transistors cause unevenness tosome extent. Thus, when a liquid crystal element or an EL element isformed on the circuits, a leveling processing using an organic resinfilm or the like is generally conducted. Each pixel which is provided ina display portion of a display device has a pixel electrode therein. Thepixel electrode is connected with the thin film transistor through acontact hole provided in the above-mentioned organic resin film forleveling.

However, the following facts are found by the studies of the presentapplicant. That is, when a resin film is used as an interlayerinsulating film and a contact hole is formed using a dry etchingtechnique, threshold voltages (Vth) of the completed thin filmtransistors are greatly varied. For example, data shown in FIGS. 4A and4B are results examined with respect to a variation in thresholdvoltages of thin film transistors formed on an SOI substrate. In thedrawings, a black circular mark indicates the case where a laminatestructure of a silicon nitride film (SiN) and an acrylic film is usedfor the interlayer insulating film. In addition, an outline triangularmark in the drawings indicates the case where a laminate structure of asilicon nitride oxide film (SiNO) and a silicon oxynitride film (SiON)is used for the interlayer insulating film. In any case, the dry etchingtechnique is used for the formation of the contact hole. Note that“SiNO” and “SiON” are separately used according to the meaning in whichthe former contains the amount of nitrogen larger than oxygen and thelatter contains the amount of oxygen larger than nitrogen.

The data shown in FIGS. 4A and 4B are graphs obtained by evaluating avariation in threshold voltages using statistical processing. Theordinate indicates a channel length (carrier moving length) and theabscissa indicates a Vth variation. In recent years, “quartiledeviation” has been known as statistical processing. The quartiledeviation is a difference between a value of 25% and a value of 75% in anormal probability graph and has been noted as statistical processingwhich is not influenced by an abnormal value. The present applicantdefines, based on the quartile deviation (which is also called 25percentile deviation), a difference between a value of 16% and a valueof 84% as 16 percentile deviation, and plots its value as “a Vthvariation” in the abscissa. Note that the 16 percentile deviationcorresponds to ±σ in a normal probability distribution. Thus, values,which are assumed as ±3σ by respectively multiplying by factors, areused for data plotting. When an acrylic film is used as an interlayerinsulating film, as seen from the data, a variation in an n-channel TFTis about 4 times and a variation in a p-channel TFT is about 2 timesthose of the case not using the acrylic film. Thus, it is apparent thata variation is large in the case where the acrylic film is used. Thepresent applicant estimates that a charge is captured in the acrylicfilm by plasma damage in dry etching, thereby providing a cause ofvarying a threshold voltage.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentionedproblems, and has an object to provide a technique for producing a thinfilm transistor without varying its threshold voltage in manufacturing adisplay device using an organic resin film as an interlayer insulatingfilm, and achieve the improvement of operating performance stability ofthe display device and an increase of a design margin in a circuitdesign. In addition, another object of the present invention is toachieve the improvement of image quality of the display device.

The present invention is characterized to solve the above problems bythe following means. That is, it has such a feature that aphotosensitive organic resin film (preferably, a photosensitive acrylicfilm, particularly, a positive type photosensitive acrylic film) is usedas an organic resin film, a first opening is formed in thephotosensitive organic resin film, a nitride insulating film coveringthe first opening is formed, a second opening is formed in the nitrideinsulating film using a photo resist or the like, and an upper electrodeand a lower electrode which are located to sandwich the organic resinfilm are electrically connected with each other. Note that, when thepositive type photosensitive acrylic film is used, it is generallycolored with light brown. Thus, it is required that decolorizationprocessing (bleaching processing) is conducted, so that it is madetransparent with respect to visible light after the first opening isprovided. In the decolorization processing, light used for exposure tothe entire pattern after development (typically, ultraviolet light) ispreferably irradiated.

The present invention will be described using FIGS. 1A and 1B. In FIG.1A, reference numeral 101 denotes a substrate, 102 denotes a base film,103 denotes a source region, 104 denotes a drain region, and 105 denotesa channel formation region. The source region, the drain region, and thechannel formation region which are provided on the base film 102 aremade from a semiconductor film. In addition, reference numeral 106denotes a gate insulating film, 107 denotes a gate electrode, and 108denotes a first passivation film. A known thin film transistor structureis described up to here. Various known materials can be used formaterials of respective portions.

Next, a first characteristic of the thin film transistor of the presentinvention is that a photosensitive organic resin film, particularly, apositive type photosensitive acrylic film is used as an interlayerinsulating film 109 on the first passivation film 108 that is aninorganic insulating film. A film thickness of the photosensitiveorganic resin film 109 is desirably selected from a range of 1 μm to 4μm (preferably, 1.5 μm to 3 μm). A second characteristic is that a firstopening portion (indicated by a diameter of φ1) 110 is provided in thephotosensitive organic resin film 109 and a second passivation film 111that is an inorganic insulating film is provided so as to cover the topsurface of the photosensitive organic resin film 109 and the inner wallsurface of the first opening portion 110. Further, a thirdcharacteristic is that the second passivation film 111 has a secondopening portion (indicated by a diameter of φ2) 112 in the bottom of thefirst opening portion 110 and an opening portion having the samediameter as the second opening portion 112 is formed in the firstpassivation film 108 and the gate insulating film 106. In other words,it has such a feature that the second opening portion is provided in alaminate including the gate insulating film 106, the first passivationfilm 108, and the second passivation film 111 inside the first openingportion 110. In addition, a source electrode 113 is connected with thesource region 103 through the first opening portion 110 and the secondopening portion 112. A drain electrode 114 is similarly connected withthe drain region 104.

Note that a silicon nitride film, a silicon nitride oxide film, asilicon oxynitride film, an aluminum nitride film, an aluminum nitricoxide film, or an aluminum oxynitride film can be used for the firstpassivation film 108 and the second passivation film 111. In addition, alaminate film including these films in at least a portion thereof can beused. It is desirable that the diameter of φ1 is set to 2 μm to 10 μm(preferably, 3 μm to 5 μm) and the diameter of φ2 is set to 1 μm to 5 μm(preferably, 2 μm to 3 μm). Note that, because a design rule of thediameters of the opening portions is changed according to precision of aphotolithography process, it is unnecessary to limit the presentinvention to these numerical ranges. In other words, in any case, it ispreferable that a relationship of φ1>φ2 is satisfied.

Here, an enlarged view of a portion of a region 115 surrounded by adotted line is shown in FIG. 1B. In FIG. 1B, a portion of the firstopening portion 110 and a portion of the second opening portion 112 areshown. With respect to the first opening portion 110, its inner wallsurface is a gradual curved surface and has a continuously changedcurvature radius. For example, when three points of curvature radii ofR1, R2, and R3 are noted in order, a relationship among the respectivecurvature radii becomes R1<R2<R3 and these numerical values each arewithin 3 μm to 30 μm (typically, 10 μm to 15 μm). In addition, an angle(contact angle θ) formed by the photosensitive organic resin film 109and the first passivation film 108 in the bottom of the first openingportion 110 is set within a range of 30° <θ<65° (typically, 40°<θ<50°).

In this time, in a portion indicated by reference numeral 116 in FIG.1B, the first passivation film 108 and the second passivation film 111are in close contact with each other, so that a state in which thephotosensitive organic resin film 109 is sealed is obtained. In thistime, it is desirable that a length of the close contact region, thatis, a length of the region in which the first passivation film 108 andthe second passivation film 111 are in contact with each other is 0.3 μmto 3 μm (preferably, 1 μm to 2 μm). Basically, it is desirable that theradius of the first opening portion 110 is larger than that of thesecond opening portion 112 by 0.3 μm to 3 μm.

There is the case where the photosensitive organic resin film used inthe present invention (here, a positive type photosensitive acrylicfilm) produces a gas component during and after the formation of a thinfilm transistor. Thus, it is very important to seal with organicinsulating films each having a sufficient close contact property(particularly, a silicon nitride film or a silicon nitride oxide filmwhich has a high barrier property is suitable) in view of preventing thedeterioration of a liquid crystal element and an EL element which areformed on the thin film transistor.

Next, a method of manufacturing the thin film transistor having thestructure shown in FIG. 1A will be described using FIGS. 2A to 2E.First, it will be described using FIG. 2A. The base film 102 is formedon the substrate 101 and an island-like semiconductor film which isprocessed by etching is formed thereon. Then, the gate insulating film106 is formed on the entire surface, the gate electrode 107 is formed,and the source region 103 and the drain region 104 are formed inself-alignment using the gate electrode 107 as a mask. At this time, thechannel formation region 105 is simultaneously determined. After theformation of the source region 103 and the drain region 104, the sourceregion 103 and the drain region 104 are activated by heat treatment.Further, the first passivation film 108 is formed and then hydrogenationprocessing is conducted by heat treatment. The manufacturing methoduntil now is preferably conducted using a known technique. Various knownmaterials can be used as materials composing the thin film transistor.Next, a photosensitive organic resin film, here, a positive typephotosensitive acrylic film is formed as the interlayer insulating film109.

Next, it will be described using FIG. 2B. After the formation of thephotosensitive organic resin film 109, exposure processing using aphotolithography process is conducted, so that the photosensitiveorganic resin film 109 is etched to form the first opening portion 110.This is a possible technique because the photosensitive organic resinfilm is used. In addition, because etching itself is wet etching using adeveloper, an effect in which a problem such as the above plasma damageis not caused is obtained. After etching using a developer,decolorization processing is conducted for the photosensitive organicresin film 109. The decolorization processing is preferably conducted byirradiating more intense light than light used for exposure to theentire pattern. Note that, it is necessary to conduct decolorizationprocessing immediately after the exposure, that is, before bakingtreatment. This is because, after baking, cross-linking of thephotosensitive organic resin film 109 is completed, so thatdecolorization by light irradiation is impossible.

Also, the first opening portion 110 becomes a cross sectional shape asshown in FIG. 1B and has a very gradually curved inner wall surface.Thus, the coverage of an electrode which is formed later becomesextremely satisfactory. Note that, in a baking process after etching, itis desirable that heating is conducted in an inert atmosphere (nitrogenatmosphere, noble gas atmosphere, or hydrogen atmosphere) in order toprevent absorption or adsorption of moisture and oxygen into a resin. Inthis time, it is desirable that an inert atmosphere is definitely keptfrom a temperature rise to a temperature fall to suppress the amount ofadsorption (or absorption) of moisture and oxygen to 10 ppm or less(preferably, 1 ppm or less).

Next, it will be described using FIG. 2C. After the formation of thefirst opening portion 110, the second passivation film 111 is formed soas to cover the top surface of the photosensitive organic resin film 109and the inner wall surface of the first opening portion 110. The samematerial as the first passivation film 108 may be used for the secondpassivation film 111. It is preferable that a sputtering method using ahigh frequency discharge is used for the formation of the secondpassivation film 111. With a condition, it is preferable that a silicontarget is used and a nitrogen gas is used as a sputtering gas. Apressure is preferably set as appropriate. It is preferable that apressure is 0.5 Pa to 1.0 Pa, discharge power is 2.5 kW to 3.5 kW, and afilm formation temperature is within a room temperature (25° C.) to 250°C. After the formation of the second passivation film 111, a photoresist 201 is formed. The photo resist 201 is a mask for forming thesecond opening portion 112 in the second passivation film 111.

Next, it will be described using FIG. 2D. After the formation of thephoto resist 201, etching processing is conducted to etch the secondpassivation film 111, the first passivation film 108, and the gateinsulating film 106 in order, thereby forming the second opening portion112. In this time, the etching processing may be dry etching processingor wet etching processing. In order that a preferable shape of thesecond opening portion 112 is obtained, dry etching processing ispreferable. According to the present invention, even when dry etchingprocessing is conducted here; there is no case where the photosensitiveorganic resin film 109 is directly exposed to plasma. Thus, a problem inwhich plasma damage is accumulated is not caused. Therefore, accordingto one of characteristics of the present invention, while the inner wallsurface of one opening portion provided in the photosensitive organicresin film are protected by a nitride insulating film such as a siliconnitride film, another opening portion having a smaller diameter isprovided in the bottom of the opening portion.

Also, when the second opening portion 112 is formed by dry etchingprocessing, the gate insulating film 106 and the first passivation film108 are etched. In this etching, productivity can be improved accordingto a combination of inorganic insulating films. In other words, when asilicon nitride film is used as the first passivation film 108 and asilicon oxynitride film is used as the gate insulating film 106, thegate insulating film 106 can serve as an etching stopper in etching thefirst passivation film 108 and the source region (silicon film) 103 canserve as an etching stopper in etching the gate insulating film 106.

For example, the case where a silicon oxynitride film is used as thegate insulating film 106 and a silicon nitride film is used as the firstpassivation film 108 is considered. The silicon nitride film serving asthe first passivation film 108 can be etched using a carbontetrafluoride (CF₄) gas, a helium (He) gas, and an oxygen (O₂) gas. Thesilicon film is also etched by these gases. However, because the siliconoxynitride film serving as the gate insulating film 106 of a base filmfunctions as an etching stopper, there is no case where the silicon filmserving as the source region 103 is lost. In addition, the gateinsulating film (here, a silicon oxynitride film) 106 can be etched byusing a trifluoromethane (CHF₃) gas and the silicon film is hardlyetched. Thus, the source region 103 can serve as an etching stopper.

Next, it will be described using FIG. 2E. After the formation of thesecond opening portion 112, a metallic film is formed thereon andpatterned by etching to form the source electrode 113 and the drainelectrode 114. In order to form these electrodes, a titanium film, atitanium nitride film, a tungsten film (including an alloy), an aluminumfilm (including an alloy), or a laminate film of those is preferablyused.

Therefore, the thin film transistor having the structure described usingFIGS. 1A and 1B can be obtained. The thus obtained thin film transistorhas a photosensitive organic resin film, and the photosensitive organicresin film also serves as a leveling film. In addition, thephotosensitive organic resin film is sealed with the nitride insulatingfilm (typically, a silicon nitride film or a silicon nitride oxidefilm), so that a problem resulting from degassing is not also caused.

Here, a reason why a positive type photosensitive acrylic film isparticularly preferable as the photosensitive organic resin film 109will be described below.

First, a photograph shown in FIG. 3A is a cross sectional SEM (scanningelectron microscope) photograph in a state in which a non-photosensitiveacrylic film (film thickness: about 1.3 μm) is processed by dry etchingto conduct patterning and FIG. 3B is its schematic view. When thenon-photosensitive acrylic film is processed by dry etching as in aconventional case, a curved surface is hardly formed in the top portionof pattern, so that the top end portion has substantially no curvatureradius (R). In addition, in the bottom portion of pattern, a taper angle(contact angle) becomes about 63°. However, a curved surface is notobserved even in the bottom end portion.

Next, a photograph shown in FIG. 5A is a cross sectional SEM photographin a state in which a positive type photosensitive acrylic film (filmthickness: about 2.0 μm) is processed by exposure and development toconduct patterning and FIG. 5B is its schematic view. With respect to across sectional shape of the positive type photosensitive acrylic film,it has a very gradually curved surface after etching processing using adeveloper and a curvature radius (R) is continuously changed. Inaddition, a small contact angle of about 32° to 33° is obtained. Inother words, the film has the shape shown in FIG. 1B itself. Thus, whenthe thin film transistor and the display device according to the presentinvention are manufactured, it can be said that such a shape is a veryuseful shape. Of course, a contact angle value is changed according toan etching condition, a film thickness, and the like. However, 30°<θ<65°is preferably satisfied as described above.

Next, a photograph shown in FIG. 6A is a cross sectional SEM photographin a state in which a negative type photosensitive acrylic film (filmthickness: about 1.4 μm) is processed by exposure and development toconduct patterning and FIG. 6B is its schematic view. With respect to across sectional shape of the negative type photosensitive acrylic film,a gradual S-shaped curved surface is formed after etching processingusing a developer and the top end portion of pattern is curved at acurvature radius (R). In addition, a contact angle value of about 47° isobtained. In this case, a length of a tail (lower slope) portionindicated by W in FIG. 6B becomes a problem. In particular, with respectto a contact hole (opening portion) for which microfabrication isrequired, when the tail portion becomes longer, there is a possibilitythat a state in which a lower layer electrode or a wiring is not exposedin the contact hole is caused, so that a disconnection resulting from apoor contact is concerned. Note that, when the length (W) of the tailportion is 1 μm or less (preferably, a length shorter than the radius ofa contact hole), a possibility of such a disconnection becomes lower.

Next, a photograph shown in FIG. 7A is a cross sectional SEM photographin a state in which a positive type photosensitive polyimide film (filmthickness: about 1.5 μm) is processed by exposure and development toconduct patterning and FIG. 7B is its schematic view. With respect to across sectional shape of the positive type photosensitive polyimidefilm, it has a slight tail portion (indicated by the length W) and acurved top end portion after etching processing using a developer.However, its curvature radius (R) is small.

When the above cross sectional shapes are observed, the following can beconsidered. When a metallic film which becomes an electrode or a wiringis formed after the formation of the contact hole (opening portion), asputtering method, an evaporation method, a CVD method, or the like isused. It has been known that material molecules composing the thin filmtransistor move toward a stable cite on a surface when they aredeposited on a surface to be formed and are easy to gather into aportion having a shape with an acute angle (shape which becomes a convexportion), such as the top end portion of the contact hole. This tendencyis remarkable in particularly an evaporation method. Therefore, when thecross sectional shape of the opening portion is the shape as shown inFIG. 3A, the material molecules gather to the edge of the openingportion, so that only its portion locally becomes thicker and aneaves-shaped convex portion is formed. This becomes a cause of a defectsuch as a disconnection (step disconnection) later and it is notpreferable. Accordingly, it can be said that the non-photosensitiveacrylic film shown in FIG. 3A and the positive type photosensitivepolyimide film shown in FIG. 7A are disadvantageous materials in view ofcoverage.

Also, as shown in FIGS. 6A and 7A above, with respect to the shape inwhich the tail portion is formed in the bottom end portion of thecontact hole, the tail portion covers the bottom surface of the contacthole in some cases and there is a possibility that a poor contact iscaused. Thus, it can be said that such films are disadvantageousmaterials in view of contact. Of course, when the length of the tailportion is 1 μm or less (preferably, a length shorter than the radius ofthe contact hole), there is no problem.

When the present invention is carried out in view of the above points,it can be said that the positive type photosensitive acrylic film withthe shape shown in FIG. 5A is most suitable. In other words, when thepositive type photosensitive acrylic film is used, it has a very gradualcurved surface in the top end portion of the contact hole. Thus, thereis completely no problem with respect to coverage. In addition, in thebottom end portion of the contact hole, the bottom surface of thecontact hole is reliably determined with a contact angle satisfying30°<θ<65° without forming the tail portion. Thus, a problem of a poorcontact is not also caused. From the above reasons, the presentapplicant considers that a positive type photosensitive acrylic film isa most preferable material to an interlayer insulating film made ofparticularly an organic resin when the present invention is carried out.

As described above, when the thin film transistor using the organicresin film as the interlayer insulating film is manufactured, thephotosensitive organic resin film is used as the interlayer insulatingfilm and the contact structure shown in FIGS. 1A and 1B is employed.Thus, the thin film transistor can be manufactured without varying thethreshold voltage. Therefore, with respect to not only the thin filmtransistor but also the display device using it, the improvement ofstability of operating performances and the increase of design margin ina circuit design can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B show a structure of a thin film transistor;

FIGS. 2A to 2E show a process of manufacturing the thin film transistor;

FIGS. 3A and 3B are an SEM photograph and a schematic view which show across sectional structure of an organic resin film;

FIGS. 4A and 4B show dispersions in threshold voltages;

FIGS. 5A and 5B are an SEM photograph and a schematic view which show across sectional structure of an organic resin film;

FIGS. 6A and 6B are an SEM photograph and a schematic view which show across sectional structure of an organic resin film;

FIGS. 7A and 7B are an SEM photograph and a schematic view which show across sectional structure of an organic resin film;

FIGS. 8A and 8B show a structure of a thin film transistor;

FIGS. 9A to 9D show a pixel structure of a light emitting device;

FIGS. 10A and 10B show cross sectional structures of the light emittingdevice;

FIGS. 11A to 11C show cross sectional structures of the light emittingdevice;

FIG. 12 shows a structure of a thin film transistor;

FIGS. 13A to 13D show a pixel structure of a liquid crystal displaydevice;

FIGS. 14A and 14B show cross sectional structures of the liquid crystaldisplay device;

FIGS. 15A to 15D show an outline structure of the light emitting device;

FIGS. 16A to 16H show specific examples of electrical appliances; and

FIGS. 17A and 17B show C-V characteristics of an MOS structure in thecase where a silicon nitride film is used as dielectric.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

In this embodiment, an example in which the formation position of thefirst opening portion 110 is changed in FIGS. 1A and 1B will bedescribed using FIGS. 8A and 8B. Note that FIGS. 8A and 8B each show across sectional structure immediately after the formation of the secondopening portion. In addition, the reference symbols used in FIGS. 1A and1B are referred to if necessary.

In FIG. 8A, reference numeral 801 denotes a first opening portion havinga diameter of φ1 and 802 denotes a second opening portion having adiameter of φ2. A characteristic in FIG. 8A is that the first openingportion 801 is provided to protrude from the end portion of the sourceregion 103. The photosensitive organic resin film 109 can be formed in aposition as indicated in this embodiment because the first passivationfilm 108 becomes an etching stopper, thereby stopping the progress ofetching. In addition, in FIG. 8B, reference numeral 803 denotes a firstopening portion having a diameter of φ3 and 804 denotes a second openingportion having a diameter of φ2. A characteristic in FIG. 8B is alsothat the first opening portion 803 is provided to protrude from the sideend portion of the source region 103. Even in this case, with respect tothe photosensitive organic resin film 109, the first passivation film108 becomes an etching stopper, thereby stopping the progress ofetching.

As described above, the inorganic insulating film which can become anetching stopper is located under the photosensitive organic resin filmused as the interlayer insulating film. Thus, even when the diameter ofthe first opening portion is increased, there is no problem, so that itis very useful because a design margin in the formation of the contacthole can be widened.

Embodiment 2

In this embodiment, an example in which the present invention is appliedto a light emitting device such as an EL display device will bedescribed. FIG. 9A is a plan view of a pixel of the light emittingelement (note that a state up to the formation of a pixel electrode isindicated), FIG. 9B is a circuit diagram thereof, and FIGS. 9C and 9Deach are a cross sectional view along a line A-A′ or B-B′.

As shown in FIGS. 9A and 9B, a display portion of the light emittingdevice includes a plurality of pixels which are surrounded by gatewirings 951, data wirings 952, and power source wirings (wirings forsupplying a constant voltage or a constant current) 953 and arranged inmatrix. In each of the pixels, a TFT 954 serving as a switching element(hereinafter referred to as a switching TFT), a TFT 955 serving as meansfor supplying a current or a voltage for producing light emission of anEL element (hereinafter referred to as a driver TFT), a capacitorportion 956, and an EL element 957 are provided. Although not shownhere, the EL element 957 can be formed by providing a light emittinglayer over a pixel electrode 958.

Note that, in this embodiment, an n-channel TFT having a multi-gatestructure is used as the switching TFT 954 and a p-channel TFT is usedas the driver TFT 955. However, it is not required that the pixelstructure of the light emitting element is limited to this. Thus, thepresent invention can be applied to various known structures.

In the cross sectional view of FIG. 9C, the n-channel TFT 954 and thecapacitor portion 956 are shown. Reference numeral 901 denotes asubstrate, and a glass substrate, a ceramic substrate, a quartzsubstrate, a silicon substrate, or a plastic substrate (including aplastic film) can be used. In addition, reference numeral 902 denotes asilicon nitride oxide film, 903 denotes a silicon oxynitride film, andthey are laminated to serve as base films. Of course, it is not requiredthat the present invention is limited to these materials. Further, anactive layer of the n-channel TFT 954 is provided on the siliconoxynitride film 903. The active layer has a source region 904, a drainregion 905, LDD regions 906 a to 906 d, and channel formation regions907 a and 907 b. In other words, it has two channel formation regionsand four LDD regions between the source region 904 and the drain region905.

Also, the active layer of the n-channel TFT 954 is covered with a gateinsulating film 908, and a gate electrode (gate electrode layers 909 aand 909 b) and another gate electrode (gate electrode layers 910 a and910 b) are provided thereon. In this embodiment, a silicon oxynitridefilm is used as the gate insulating film 908. When the above nitrideinsulating film such as an aluminum nitride film having a high relativedielectric constant is used, an occupying area of an element can bereduced. Thus, it is effective for the improvement of the scale ofintegration.

Also, a tantalum nitride film is used for the gate electrode layers 909a and 910 a and a tungsten film is used for the gate electrode layers909 b and 910 b. With respect to these metallic films, a selection ratiois high. Thus, the structure as shown in FIG. 9B can be obtained byselecting an etching condition. The etching condition is preferablyreferred to JP 2001-313397 A according to the present applicant.

Also, a silicon nitride film or a silicon nitride oxide film is providedas a first passivation film 911 covering the gate electrodes, and aphotosensitive organic resin film 912 (in this embodiment, a positivetype photosensitive acrylic film is used) is provided thereon. Further,a second passivation film 913 is provided on the photosensitive organicresin film 912 so as to cover a first opening portion (see FIG. 1A). Asecond opening portion (see FIG. 1A) is provided to the bottom of thefirst opening portion. In this embodiment, a silicon nitride film or asilicon nitride oxide film is used as the second passivation film 913.Of course, another nitride insulating film such as an aluminum nitridefilm or an aluminum nitric oxide film can be also used.

Also, the data wiring 952 is connected with the source wiring 904through the second opening portion, and a connection wiring 915 isconnected with the drain region 905 through the second opening portion.The connection wiring 915 is a wiring connected to a gate electrode ofthe driver TFT 955. A structure in which a wiring containing mainly lowresistance metal such as aluminum or copper is sandwiched by othermetallic films or an alloy film of these metals is preferably used forthe data wiring 952 and the connection wiring 915.

Also, reference numeral 916 denotes a source region of the driver TFT955, with which the power source wiring 953 is connected. In a contactportion for this connection, the first opening portion and the secondopening portion are formed by carrying out the present invention. Inaddition, the power source wiring 953 is opposite to a gate wiring 917of the driver TFT 955 through the first passivation film 911 and thesecond passivation film 913, so that a storage capacitor 956 a isformed. Further, the gate wiring 917 is opposite to a semiconductor film918 through the gate insulating film 908 so that a storage capacitor 956b is formed. Because the power source wiring 953 is connected with asemiconductor layer 919, a charge is supplied therefrom, so that thesemiconductor film 918 serves as an electrode. Thus, the capacitorportion 956 becomes a structure in which the storage capacitors 956 aand 956 b are connected in parallel, thereby obtaining a large capacitywith a very small area. Furthermore, with respect to particularly thestorage capacitor 956 a, a silicon nitride film having a high relativedielectric constant is used for dielectric, so that a large capacity canbe ensured. Because the dielectric of the storage capacity 956 a iscomposed of a laminate structure of the first passivation film 911 andthe second passivation film 913, a probability of occurrence of apinhole is extremely low. Thus, a capacitor with high reliability can beformed.

When the present invention is carried out, the number of masks used in aphotolithography process is increased to form the second opening portionas compared with a conventional case. However, when the increase in thenumber of masks is advantageously used, a new storage capacitor can beformed as described in this embodiment. Such a point is also one ofimportant characteristics of the present invention. The characteristicof the present invention more than compensates for a demerit resultingfrom the increase in the number of masks, so that it greatly contributesto industrial progress. For example, when high definition image displayis obtained, it is required that a relative occupying area of thestorage capacitor to an area of each pixel is reduced in a displayportion to improve an aperture ratio. Therefore, it is extremely usefulto increase a storage capacity.

Also, in FIG. 9D, reference numeral 920 denotes a drain region of thedriver TFT 955, which is connected with a drain wiring 921. The drainwiring 921 is connected with a pixel electrode 958 to compose a pixel.In this embodiment, an oxide conductive film which is transparent withrespect to visible light (typically, an ITO film) is used as the pixelelectrode 958. However, the present invention is not limited to such afilm.

An example after an EL element is actually formed in the light emittingdevice having the above pixel structure is shown in FIGS. 10A and 10B.FIG. 10A is a cross sectional view corresponding to the cross sectionshown in FIG. 9D and shows a state in which the EL element 957 is formedon the pixel electrode 958. Note that, when the structure shown in FIG.10A is used, the pixel electrode 958 corresponds of the anode of the ELelement 957. In addition, in this specification, an EL element indicatesan element in which an EL layer is provided between a cathode and ananode and a voltage is applied to the EL layer or a current is injectedthereto to emit light.

The end portion of the pixel electrode 958 is covered with aphotosensitive organic resin film 961. The photosensitive organic resinfilm 961 is provided in a grid shape so as to frame each pixel orprovided in a stripe shape in row unit or column unit. In any case, whenit is formed on the contact hole, a concave portion can be efficientlyembedded and the entire surface can be also leveled. Note that, in thisembodiment, the same material as the photosensitive organic resin film(first photosensitive organic resin film) 912 used as the interlayerinsulating film described above (in this embodiment, the positive typephotosensitive acrylic film) is used for the photosensitive organicresin film (second photosensitive organic resin film) 961. Thus,manufacturing facilities can be minimized. In addition, although notshown, the negative type photosensitive acrylic film which becomes anS-shaped cross section as shown in FIGS. 6A and 6B may be used. Ofcourse, in this time, it is desirable that a curvature radius in a topend portion and a bottom end portion of the opening portion is set to 3μm to 30 μm (typically, 10 μm to 15 μm). In addition, in this case, whena length of the tail portion indicted by W is not minimized, it is notpreferable because an aperture ratio is reduced. Further, a known resistmaterial (polymer material containing chromophore) can be also used.

Also, the surface of the photosensitive organic resin film 961 iscovered with a nitride insulating film as a third passivation film 962,so that degassing from the photosensitive organic resin film 961 can besuppressed. In addition, the third passivation film 962 is etched on thepixel electrode 958 to provide an opening portion. In the openingportion, an EL layer 963 is in contact with the pixel electrode 958. TheEL layer 963 is generally composed by laminating thin films such as alight emitting layer, a charge injecting layer, and a chargetransporting layer. However, various structures and various materials inwhich light emission has been observed can be used. For example, SAlq(in which one of three ligands of Alq₃ is substituted for atriphenylsilanol structure) as an organic system material containingsilicon can be also used as a charge transporting layer or a holeblocking layer.

Of course, the EL layer is not necessarily composed of only organic thinfilm, and a structure in which an organic thin film and an inorganicthin film are laminated may be also used. A polymer thin film or a lowmolecular thin film may be used. In addition, a forming method ischanged according to whether a polymer thin film or a low molecular thinfilm is used. However, the thin film is preferably formed by a knownmethod.

Also, a cathode 964 is formed on the EL layer 963, and a nitrideinsulating film as a fourth passivation film 965 is finally providedthereon. A metallic thin film containing an element belonging to group 1or 2 of the periodic table is preferably used as the cathode 964. Ametallic film in which lithium of 0.2 wt % to 1.5 wt % (preferably, 0.5wt % to 1.0 wt %) is added to aluminum is suitable in view of a chargeinjecting property and the like. Note that, if lithium is diffused, itis concerned that the operation of a TFT is influenced thereby. However,according to this embodiment, the TFT is completely protected by thefirst passivation film 911, the second passivation film 913, and thethird passivation film 962, so that it is unnecessary to concern thediffusion of lithium.

Here, data indicating a blocking effect of a silicon nitride film formedby a sputtering method using high frequency discharge with respect tolithium are shown in FIGS. 17A and 17B. FIG. 17A shows a C-Vcharacteristic of an MOS structure in the case where a silicon nitridefilm formed by a sputtering method using high frequency discharge(indicated as RF-SP SiN) is used as dielectric. Note that “Li-dip” meansthat a solution containing lithium is spin-coated on the silicon nitridefilm and means that contamination is intentionally caused using lithiumfor a test. In addition, FIG. 17B shows a C-V characteristic of an MOSstructure in the comparative case where a silicon nitride film formed bya plasma CVD method (indicated as CVD SiN) is used as dielectric. Notethat, with respect to data shown in FIG. 17B, an alloy film in whichlithium is added to aluminum is used as a metallic electrode. A generalBT test is conducted for these films (specifically, heat treatment isconducted at ±150° C. for 1 hour in addition to the application of avoltage of 1.7 MV). As a result, as shown in FIG. 17A, a change in C-Vcharacteristic in the case where the silicon nitride film formed by thesputtering method using high frequency discharge is hardly observed. Onthe other hand, a large change in C-V characteristic in the case wherethe silicon nitride film formed by the plasma CVD method is observed.Accordingly, contamination of lithium is recognized. These data suggestthat the silicon nitride film formed by the sputtering method using highfrequency discharge has a very effective blocking effect to lithiumdiffusion.

Further, when a nitride insulating film is used as the secondpassivation film 913 or the third passivation film 962, a heat radiationeffect can be expected. For example, if it is assumed that a thermalconductivity of a silicon oxide film is 1, that of a silicon nitridefilm is about 5 and that of an aluminum nitride film is about 35 to 130,thereby obtaining a very high thermal conductivity. Thus, even when theEL element generates heat, heat is effectively radiated, so that thedeterioration of the EL layer 963 resulting from self heat radiation canbe suppressed.

Note that the same material as the nitride insulating film used for thefirst passivation film 911 and the second passivation film 913 can beused for the third passivation film 962 and the fourth passivation film965.

When the structure shown in FIG. 10A is used, light emitted from the ELelement transmits the pixel electrode 958 and exits from the substrate901 side. At this time, the transmitting light transmits through thephotosensitive organic resin film 912. Thus, it is required thatsufficient decolorization processing is conducted for the photosensitiveorganic resin film 912 so that it is made sufficiently transparent.

Next, FIG. 10B shows an example in which a metallic film 971 having areflecting property is used instead of the pixel electrode 958. As themetallic film 971 having the reflecting property, a film of metal suchas platinum (Pt) or gold (Au) having a high work function is used toserve as an anode. In addition, because such a metal is expensive, itmay be laminated on a suitable metallic film such as an aluminum film ora tungsten film to form a pixel electrode in which at least platinum orgold is exposed onto an uppermost surface. Reference numeral 972 denotesan EL layer, and various structures and various materials in which lightemission has been observed can be used as in the case shown in FIG. 10A.In addition, reference numeral 973 denotes a metallic film having asmall film thickness (preferably, 10 nm to 50 nm). A metallic filmcontaining an element belonging to group 1 or 2 of the periodic table isused to serve as a cathode. Further, an oxide conductive film(typically, an ITO film) 974 is provided by laminating it on themetallic film 973 and a fourth passivation film 975 is provided thereon.

When the structure shown in FIG. 10B is used, light emitted from the ELelement is reflected by the pixel electrode 971, transmits through themetallic film 973, the oxide conductive film 974, and the like, andexits from the substrate. At this time, because the light does nottransmit through a portion under the pixel electrode 971, a memoryelement, a resistor element, or the like may be provided therein and thephotosensitive organic resin film 912 may be colored. Thus, a degree offlexibility in a design is high and a manufacturing process can be alsosimplified. Therefore, it can be said that the structure generallycontributes to a reduction in manufacturing cost.

Embodiment 31

In this embodiment, an example is indicated in which a connectionstructure between the drain wiring 921 and the pixel electrode 958 ismodified in the light emitting device described in Embodiment 2. Notethat the fundamental structure is not changed as compared with thatshown in FIG. 9C. Thus, in this embodiment, reference symbols areprovided to only necessary portions and the description will be made.

As shown in FIG. 11A, a pixel electrode 501 made from an oxideconductive film is formed and then a drain wiring 502 is formed, so thata structure in which the drain wiring 502 is in contact with the pixelelectrode 501 so as to cover the end portion thereof is obtained. Whensuch a structure is obtained, the pixel electrode 501 may be formedafter the formation of a second opening portion 503. Alternatively, thesecond opening portion 503 may be formed after the formation of thepixel electrode 501. In any case, even when dry etching processing isconducted, the photosensitive organic resin film 912 is always protectedby the second passivation film 913 from plasma damage. Thus, there is nocase where electrical characteristics of a thin film transistor areadversely influenced.

Next, as shown in FIG. 11B, an interlayer insulating film 504 made froman inorganic insulating film is provided on the first passivation film911, and a drain wiring 505 is provided thereon. A connection wiring 506is formed simultaneous with the drain wiring. The connection wiring 506is connected with a capacitor wiring 917 of a lower layer. The drainwiring 505 and the connection wiring 506 are covered with aphotosensitive organic resin film 508 having a first opening portion507. The first opening portion 507 is covered with a second passivationfilm 509 made from a nitride insulating film. The second passivationfilm 509 has a second opening portion 510 in the bottom of the firstopening portion 507. A pixel electrode 511 made from an oxide conductivefilm are connected with the drain wiring 505 through the first openingportion 507 and the second opening portion 510.

In this time, a storage capacitor 512 which is composed of theconnection wiring 506, the second passivation film 509, and the pixelelectrode 511 is produced on the connection wiring 506. In the case ofthe structure shown in FIG. 11B, only the second passivation film 509having a high relative dielectric constant is used as dielectric, sothat a storage capacitor having a large capacitance value can beproduced. Of course, a storage capacitor using the pixel electrode 511and the capacitor wiring 917 as a pair of electrodes can be alsoproduced. However, in this case, because the second passivation film509, the interlayer insulating film 504, and the first passivation film911 are used as dielectric, a capacitance value becomes lower than thatin the structure shown in FIG. 11B.

Next, FIG. 11C shows an example in which a nitride insulating film 513is provided as another passivation film after the formation of the drainwiring 505 and the connection wiring 506 in FIG. 11B. In such a case, astorage capacitor 514 is composed of the connection wiring 506, thenitride insulating film 513, the second passivation film 509, and thepixel electrode 511. In this case, the film thickness is increased ascompared with that in FIG. 11B, thereby slightly reducing a capacitancevalue. However, when a laminate is used for dielectric, a problemrelated to a pinhole, and the like can be reduced, so that thereliability of the storage capacitor is improved.

As described above, the present invention is not limited to thestructure described in Embodiment 2, and therefore can be applied tovarious transistor structures using the organic resin film as theinterlayer insulating film. Note that, in the structure described inthis embodiment, the nitride insulating film described in Embodiments 1and 2 above can be used for the second passivation film 509 and thenitride insulating film 513.

Embodiment 4

In this embodiment, an example in which a bottom gate thin filmtransistor (specifically, an inverse staggered TFT) is used as a thinfilm transistor in Embodiments 1 to 3 will be described. In other words,even when an inverse staggered TFT is used for the switching TFT and thedriver TFT in Embodiment 2 or 3, the present invention can be carriedout.

This embodiment will be described using FIG. 12. In FIG. 12, referencenumeral 301 denotes a substrate, 302 denotes a gate electrode, 303denotes a gate insulating film, 304 denotes a source region, 305 denotesa drain region, 306 a and 306 b denote LDD regions, and 307 denotes achannel formation region. The source region, the drain region, the LDDregions, and the channel formation region are made from a semiconductorfilm provided on the gate insulating film 302 covering the gateelectrode 302. In addition, reference numerals 308 and 309 denoteinorganic insulating films. In this embodiment, 308 denotes a siliconoxide film and 309 denotes a silicon nitride film. The silicon nitridefilm 309 serves as a first passivation film. The silicon oxide film 308serves as a buffer layer between a semiconductor layer which becomes alower layer and the first passivation film 309 made of silicon nitride.A known thin film transistor structure is described up to here. Variousknown materials can be used for materials of respective portions.

Next, a photosensitive organic resin film, specifically, a positive typephotosensitive acrylic film is provided as an interlayer insulating film310 on the first passivation film 309. A first opening portion(indicated by a diameter of φ1) 311 is provided in the photosensitiveorganic resin film 310. Further, a second passivation film 312 made froman inorganic insulating film is provided so as to cover the top surfaceof the photosensitive organic resin film 310 and the inner wall surfaceof the first opening portion 311. A second opening portion (indicated bya diameter of φ2) 313 is provided in the second passivation film 312 inthe bottom of the first opening portion 311. Reference numeral 314denotes a source electrode and 315 denotes a drain electrode.

Even in this embodiment, as in Embodiment 1, a silicon nitride film, asilicon nitride oxide film, a silicon oxynitride film, an aluminumnitride film, an aluminum nitric oxide film, or an aluminum oxynitridefilm can be used for the first passivation film 309 and the secondpassivation film 312. In addition, a laminate film including these filmsin at least a portion thereof can be used. It is desirable that thediameter of φ1 is set to 2 μm to 10 μm (preferably, 3 μm to 5 μm) andthe diameter of φ2 is set to 1 μm to 5 μm (preferably, 2 μm to 3 μm). Itis preferable that a relationship of φ1>φ2 is satisfied. Note that,because the cross sectional shape of the first opening portion 311 hasbeen described in detail in “Summary of the Invention”, it is omittedhere. It is desirable that an inner wall surface of the first openingportion is a gradual curved surface and has a continuously changedcurvature radius. Specifically, when three points of curvature radii ofR1, R2, and R3 are noted in order, it is desirable that a relationshipamong the respective curvature radii becomes R1<R2<R3 and thesenumerical values each become within 3 μm to 30 μm (typically, 10 μm to15 μm). In addition, an angle (contact angle θ) formed by thephotosensitive organic resin film 310 and the first passivation film 309in the bottom of the first opening portion 311 is preferably kept withina range of 30°<θ<65° (typically, 40°<θ<50°.

As described above, when the present invention is carried out, thestructure of a thin film transistor is not necessarily limited to only atop gate type or only a bottom gate type. Thus, the present inventioncan be applied to a thin film transistor having any structure. Further,the present invention is not necessarily limited to a thin filmtransistor, and may be applied to a transistor having a MOS structurewhich is formed using a silicon well.

Embodiment 5

In this embodiment, an example in which the present invention is appliedto a liquid crystal display device will be described. FIG. 13A is a planview of a pixel of a liquid crystal display device (note that a state upto the formation of a pixel electrode is indicated), FIG. 13B is acircuit diagram thereof, and FIGS. 13C and 13D each are a crosssectional view along a line A-A′ or B-B′.

As shown in FIGS. 13A and 13B, a display portion of the liquid crystaldisplay device includes a plurality of pixels which are surrounded bygate wirings 851 and data wirings 852 and arranged in matrix. In each ofthe pixels, a TFT 853 serving as a switching element (hereinafterreferred to as a switching TFT), a capacitor portion 854, and a liquidcrystal element 855 are provided. In the circuit shown in FIG. 13B, boththe capacitor portion 854 and the liquid crystal element 855 areconnected with a constant potential line 856. However, they are notnecessarily kept to the same potential, i.e., one may be kept to acommon potential and the other may be kept to a ground potential (earthpotential). In addition, although not shown here, the liquid crystalelement can be formed by providing a liquid crystal layer over a pixelelectrode 857. Note that, although in this embodiment, an n-channel TFThaving a multi-gate structure is used as the switching TFT 853, ap-channel TFT may alternatively be used. The layout of the switching TFTis preferably determined as appropriate by an operator.

In the cross sectional view of FIG. 13C, the switching TFT 853 and thecapacitor portion 854 are shown. Reference numeral 801 denotes asubstrate, and a glass substrate, a ceramic substrate, a quartzsubstrate, a silicon substrate, or a plastic substrate (including aplastic film) can be used. In addition, reference numeral 802 denotes asilicon nitride oxide film, 803 denotes a silicon oxynitride film, andthey are laminated to serve as base films. Of course, the presentinvention is not necessarily limited to these materials. Further, anactive layer of the switching TFT 853 is provided on the siliconoxynitride film 803. The active layer has a source region 804, a drainregion 805, LDD regions 806 a to 806 d, and channel formation regions807 a and 807 b. In other words, it has two channel formation regionsand four LDD regions between the source region 804 and the drain region805.

Also, the active layer of the switching TFT 853 is covered with a gateinsulating film 808, and a gate electrode (gate electrode layers 809 aand 809 b) and another gate electrode (gate electrode layers 810 a and810 b) are provided thereon. In this embodiment, a silicon oxynitridefilm is used as the gate insulating film 808. In addition, a tantalumnitride film is used for the gate electrode layers 809 a and 810 a and atungsten film is used for the gate electrode layers 809 b and 810 b.With respect to these metallic films, a selection ratio is high. Thus,the structure as shown in FIG. 13B can be obtained by selecting anetching condition. The etching condition may be referred to JP2001-313397 A according to the present applicant.

Also, a silicon nitride film or a silicon nitride oxide film is providedas a first passivation film 811 covering the gate electrodes, and aphotosensitive organic resin film 812 (in this embodiment, a positivetype photosensitive acrylic film is used) is provided thereon. Further,a second passivation film 813 is provided on the photosensitive organicresin film 812 so as to cover a first opening portion (see FIG. 1A). Asecond opening portion (see FIG. 1A) is provided to the bottom of thefirst opening portion. In this embodiment, a silicon nitride film or asilicon nitride oxide film is used as the second passivation film 813.Of course, another nitride insulating film such as an aluminum nitridefilm or an aluminum nitric oxide film can be also used.

Also, the data wiring 852 is connected with the source region 804through the first opening portion, and the drain wiring 815 is connectedwith the drain region 805 through the second opening portion. The drainwiring 815 is used as an electrode composing a storage capacitor in thecapacitor portion and electrically connected with the pixel electrode857. Note that, in this embodiment, an oxide conductive film which istransparent with respect to visible light (typically, an ITO film) isused as the pixel electrode 857. However, the present invention is notlimited to such a film. In addition, a structure in which a wiringcontaining mainly low resistance metal such as aluminum or copper issandwiched by other metallic films or an alloy film of these metals ispreferably used for the data wiring 852 and the drain wiring 815.

The drain wiring 815 is opposite to a capacitor wiring 816 which isformed together with the gate electrodes (that is, which is formed onthe same surface as the gate electrodes) through the first passivationfilm 811 and the second passivation film 813, so that a storagecapacitor 854 a is produced. Further, the capacitor wiring 816 isopposite to a semiconductor film 817 through the gate insulating film808 so that a storage capacitor 854 b is produced. Because thesemiconductor film 817 is electrically connected with the drain region805, when a constant voltage is applied to the capacitor wiring 816, thesemiconductor film serves as an electrode. Thus, the capacitor portion854 becomes a structure in which the storage capacitors 854 a and 854 bare connected in parallel, thereby obtaining a large capacity with avery small area. Furthermore, with respect to particularly the storagecapacitor 854 a, a silicon nitride film having a high relativedielectric constant is used for dielectric, so that a large capacity canbe ensured.

An example, up to the actual formation of a liquid crystal element ofthe liquid crystal display device having the above pixel structure isshown in FIGS. 14A and 14B. FIG. 14A is a cross sectional viewcorresponding to the cross section shown in FIG. 13C and shows a statein which the liquid crystal element 855 is formed on the pixel electrode857. A spacer 821 made of an organic resin is provided on the drainwiring 815, and an alignment film 822 is provided thereon. The formationorder of the spacer 821 and the alignment film 822 may be reverse.Further, a light shielding film 824 made from a metallic film, a counterelectrode 825 made from an oxide conductive film, and an alignment film826 are provided on another substrate (counter substrate) 823, and thenthe alignment film 822 and the alignment film 826 are bonded opposite toeach other using a sealing material (not shown). Furthermore, a liquidcrystal 827 is injected from a liquid crystal injection port provided inthe sealing material, and the liquid crystal injection port is thensealed to complete the liquid crystal display device. Note that ageneral liquid crystal cell assembly process is preferably applied to aprocess after the formation of the spacer 821. Thus, the detaileddescription is not particularly made.

When the structure shown in FIG. 14A is used, light is made incidentfrom the counter substrate 823 side, modulated through the liquidcrystal 827, and exits from the substrate 801 side. At this time, thetransmitting light transmits through the photosensitive organic resinfilm 812 used as the interlayer insulating film. Thus, it is requiredthat sufficient decolorization processing is conducted for thephotosensitive organic resin film 812 so that it is made sufficientlytransparent.

Next, FIG. 14B shows an example in which a drain wiring 831 made from ametallic film having a reflecting property is used without modificationinstead of the pixel electrode 857. As the metallic film having thereflecting property, an aluminum film (including an aluminum alloy film)or a conductive film having a silver thin film at least on its surfacecan be used. The description related to other portions for which thesame reference symbols as in FIG. 14A are provided is omitted here. Whenthe structure shown in FIG. 14B is used, light is made incident from thecounter substrate 823 side, modulated through the liquid crystal 827,and outputted from the counter substrate 823 side again. At this time,because the light does not transmit through a portion under the drainwiring 831, a memory element, a resistor element, or the like may beprovided therein and the photosensitive organic resin film 812 may becolored. Thus, a degree of flexibility in a design is high and amanufacturing process can be also simplified. Therefore, it can be saidthat the structure generally contributes to a reduction in manufacturingcost.

Embodiment 6

In this embodiment, a structure of the entire light emitting deviceshown in FIGS. 9A to 9D will be described using FIGS. 15A to 15D. FIG.15A is a plan view of a light emitting device produced by sealing anelement substrate in which thin film transistors are formed with asealing material. FIG. 15B is a cross sectional view along a line B-B′in FIG. 9A. FIG. 15C is a cross sectional view along a line A-A′ in FIG.15A.

A pixel portion (display portion) 402, a data line driver circuit 403,gate line driver circuits 404 a and 404 b, and a protective circuit 405,which are provided to surround the pixel portion 402, are located on asubstrate 401, and a seal material 406 is provided to surround them. Thestructure of the pixel portion 402 preferably refers to FIGS. 10A and10B and its description. As the seal material 406, a glass material, ametallic material (typically, a stainless material), a ceramic material,or a plastic material (including a plastic film) can be used. As shownin FIGS. 10A and 10B, it can be also sealed with only an insulatingfilm. In addition, it is necessary to use a translucent materialaccording to a radiation direction of light from an EL element.

The seal material 406 may be provided to partially overlap with the dataline driver circuit 403, the gate line driver circuits 404 a and 404 b,and the protective circuit 405. A sealing material 407 is provided usingthe seal material 406, so that a closed space 408 is produced by thesubstrate 401, the seal material 406, and the sealing material 407. Ahygroscopic agent (barium oxide, calcium oxide, or the like) 409 isprovided in advance in a concave portion of the sealing material 407, sothat it has a function of absorbing moisture, oxygen, and the like tokeep an atmosphere clean in an inner portion of the above closed space408, thereby suppressing the deterioration of an EL layer. The concaveportion is covered with a cover material 410 with a fine mesh shape. Thecover material 410 allows air and moisture to pass therethrough but notthe hygroscopic agent 409. Note that the closed space 408 is preferablyfilled with a noble gas such as nitrogen or argon, and can be alsofilled with a resin or a liquid if it is inert.

Also, an input terminal portion 411 for transmitting signals to the dataline driver circuit 403 and the gate line driver circuits 404 a and 404b is provided on the substrate 401. Data signals such as video signalsare transferred to the input terminal portion 411 through a FPC(flexible printed circuit) 412. With respect to a cross section of theinput terminal portion 411, as shown in FIG. 15B, an input wiring havinga structure in which an oxide conductive film 414 is laminated on awiring 413 formed together with a gate wiring or, a data wiring iselectrically connected with a wiring 415 provided in the FPC 412 sidethrough a resin 417 to which conductors 416 are dispersed. Note that aspherical polymer compound for which plating processing using gold orsilver is conducted is preferably used for the conductors 416.

Also, an enlarged view of a region 418 surrounded by a dot line in FIG.15C is shown in FIG. 15D. The protective circuit 405 is preferablycomposed by combining a thin film transistor 419 and a capacitor 420,and any known structure may be used therefor. The present invention hassuch a feature that the formation of the capacitor is possible withoutincreasing the number of photolithography steps together with, theimprovement of contact holes. In this embodiment, the capacitor 420 isformed utilizing the feature. Note that the structure of the thin filmtransistor 419 and that of the capacitor 420 can be understood if FIGS.10A and 10B and description thereof are referred to, and therefore thedescription is omitted here.

In this embodiment, the protective circuit 405 is provided between theinput terminal portion 411 and the data line driver circuit 403. When anelectrostatic signal such as an unexpected pulse signal is inputtedtherebetween, the protective circuit releases the pulse signal to theoutside. At this time, first, a high voltage signal which isinstantaneously inputted can be dulled by the capacitor 420, and otherhigh voltages can be released to the outside through a circuit composedof a thin film transistor and a thin film diode. Of course, theprotective circuit may be provided in other location, for example, alocation between the pixel portion 402 and the data line driver circuit403 or locations between the pixel portion 402 and the gate line drivercircuits 404 a and 404 b.

As described above, according to this embodiment, when the presentinvention is carried out, an example in which the capacitor used for theprotective circuit for electrostatic measures and the like which isprovided in the input terminal portion is simultaneously formed isindicated. This embodiment can be carried out by being combined with anystructure of Embodiments 1 to 5.

Embodiment 7

Examples of electronics employing a display apparatus of the presentinvention to a display portion are: a video camera; a digital camera; agoggle type display (head mounted display); a navigation system; anaudio reproducing apparatus (car audio, an audio component, and thelike); a laptop computer; a game machine; a portable informationterminal (a mobile computer, a cellular phone, a portable game machine,an electronic book, etc.); and an image reproducing apparatus includinga recording medium (specifically, an appliance capable of processingdata in a recording medium such as a Digital Versatile Disk (DVD) andhaving a display apparatus that can display the image of the data).Specific examples of the electronics are shown in FIGS. 16A to 16H.

FIG. 16A shows a television, which comprises a casing 2001, a supportingbase 2002, a display unit 2003, speaker units 2004, a video inputterminal 2005, etc. The present invention is applied to the display unit2003. The term television includes every television for displayinginformation such as one for a personal computer, one for receiving TVbroadcasting, and one for advertisement.

FIG. 16B shows a digital camera, which comprises a main body 2101, adisplay unit 2102, an image receiving unit 2103, operation keys 2104, anexternal connection port 2105, a shutter 2106, etc. The presentinvention is applied to the display unit 2102.

FIG. 16C shows a laptop computer, which comprises a main body 2201, acasing 2202, a display unit 2203, a keyboard 2204, an externalconnection port 2205, a pointing mouse 2206, etc. The present inventionis applied to the display unit 2203.

FIG. 16D shows a mobile computer, which comprises a main body 2301, adisplay unit 2302, a switch 2303, operation keys 2304, an infrared rayport 2305, etc. The present invention is applied to the display unit2302.

FIG. 16E shows a portable image reproducing apparatus equipped with arecording medium (a DVD player, to be specific). The apparatus comprisesa main body 2401, a casing 2402, a display unit A 2403, a display unit B2404, a recording medium (such as DVD) reading unit 2405, operation keys2406, speaker units 2407, etc. The display unit A 2403 mainly displaysimage information whereas the display unit B 2404 mainly displays textinformation. The present invention is applied to the display units A2403 and B 2404. The term image reproducing apparatus equipped with arecording medium includes domestic game machines.

FIG. 16F shows a goggle type display (head mounted display), whichcomprises a main body 2501, display units 2502, and arm units 2503. Thepresent invention is applied to the display unit 2502.

FIG. 16G shows a video camera, which comprises a main body 2601, adisplay unit 2602, a casing 2603, an external connection port 2604, aremote control receiving unit 2605, an image receiving unit 2606, abattery 2607, an audio input unit 2608, operation keys 2609, etc. Thepresent invention is applied to the display portion 2602.

FIG. 16H shows a cellular phone, which comprises a main body 2701, acasing 2702, a display unit 2703, an audio input unit 2704, an audiooutput unit 2705, operation keys 2706, an external connection port 2707,an antenna 2708, etc. The present invention is applied to the displayunit 2703. If the display unit 2703 displays white characters on a blackbackground, power consumption of the cellular phone can be reduced.

As described above, the display apparatus obtained by applying thepresent invention may be used as the display units of every electronics.Low-cost display apparatus can be provided and the electronics partscost can be lowered. Since the stability of the performance of thedisplay apparatus can be improved and the design margin in the circuitdesign can be expanded in the present invention, the low-cost displayapparatus can be provided and the electronics parts cost can be lowered.Also, the electronics of the present Embodiment may use anyconfiguration of the display apparatuses shown in Embodiments 1 to 6.

According to the present invention, a display device can be manufacturedwithout varying a threshold voltage of a thin film transistor by aprocess having a high design margin in a circuit design, so that theimprovement of stability of operating performance of the display devicecan be achieved. Further, a large capacitor can be produced with a smallarea together with the above thin film transistor without increasing thenumber of photolithography steps, thereby improving an image quality ofthe display device.

1. (canceled)
 2. A display device comprising: a substrate; a flexibleprinted circuit affixed to the substrate; a transistor on the substrate,the transistor being electrically connected to the flexible printedcircuit; a semiconductor layer comprising a first region and a secondregion, the first region constituting a channel formation region of thetransistor; a first conductive layer on and in direct contact with thesecond region of the semiconductor layer; an organic insulating filmover the first conductive layer; an inorganic insulating film over theorganic insulating film and in a first opening portion formed in theorganic insulating film; and a second conductive layer over theinorganic insulating film, on and in direct contact with the firstconductive layer in the first opening portion formed in the organicinsulating film and in a second opening portion formed in the inorganicinsulating film, wherein the first opening and the second opening eachoverlap a same portion of the substrate, and wherein the secondconductive layer is a pixel electrode of a pixel.
 3. The display deviceaccording to claim 2, wherein the organic insulating film is on and indirect contact with the first conductive layer, wherein the inorganicinsulating film is on and in direct contact with the organic insulatingfilm and with the first conductive layer, and wherein the secondconductive layer is on and in direct contact with the inorganicinsulating film.
 4. The display device according to claim 2, wherein,when seen in a cross sectional view of the first opening portion and thesecond opening portion, an entirety of the second opening portionoverlaps with the first opening portion.
 5. The display device accordingto claim 2, wherein, when seen in a cross sectional view of the firstopening portion and the second opening portion, a surface of the organicinsulating film shaping an inner wall of the second opening has acurvature radius continuously changed in the range of 3 μm to 30 μm. 6.The display device according to claim 2, wherein the organic insulatingfilm is made from a positive type photosensitive film.
 7. The displaydevice according to claim 2, wherein a surface of the organic insulatingfilm shaping an inner wall of the second opening has a continuouslychanged curvature radius, and wherein a contact angle formed by thesurface of the organic insulating film in the second opening with abottom surface of the second opening is within a range of 30° to 65°. 8.A display device comprising: a substrate; a flexible printed circuitaffixed to the substrate; a transistor on the substrate, the transistorbeing electrically connected to the flexible printed circuit; asemiconductor layer comprising a first region and a second region, thefirst region constituting a channel formation region of the transistor;a first conductive layer on and in direct contact with the second regionof the semiconductor layer; a first inorganic insulating film over thefirst conductive layer; an organic insulating film over the firstinorganic insulating film and the first conductive layer; a secondinorganic insulating film over the organic insulating film and in afirst opening portion formed in the organic insulating film; and asecond conductive layer over the second inorganic insulating film, onand in direct contact with the first conductive layer in the firstopening portion formed in the organic insulating film, in a secondopening portion formed in the first inorganic insulating film, and in athird opening portion formed in the second inorganic insulating film,wherein the first opening portion, the second opening portion, and thethird opening portion each overlap a same portion of the substrate, andwherein the second conductive layer is a pixel electrode of a pixel. 9.The display device according to claim 8, wherein the first inorganicinsulating film is on and in direct contact with the first conductivelayer, wherein the organic insulating film is on and in direct contactwith the first inorganic insulating film, wherein the second inorganicinsulating film is on and in direct contact with the organic insulatingfilm, and wherein the second conductive layer is on and in directcontact with the second inorganic insulating film.
 10. The displaydevice according to claim 8, wherein, when seen in a cross sectionalview of the first opening portion, the second opening portion, and thethird opening portion, an entirety of the second opening portion and anentirety of the third opening portion overlap with the first openingportion.
 11. The display device according to claims 8, wherein, whenseen in a cross sectional view of the first opening portion, the secondopening portion, and the third opening portion, a surface of the organicinsulating film shaping an inner wall of the second opening has acurvature radius continuously changed in the range of 3 μm to 30 μm. 12.The display device according to claim 8, wherein the organic insulatingfilm is made from a positive type photosensitive film.
 13. The displaydevice according to claim 8, wherein a surface of the organic insulatingfilm shaping an inner wall of the second opening has a continuouslychanged curvature radius, and wherein a contact angle formed by thesurface of the organic insulating film in the second opening with abottom surface of the second opening is within a range of 30° to 65°.14. A display device comprising: a substrate; a flexible printed circuitaffixed to the substrate; a transistor on the substrate, the transistorbeing electrically connected to the flexible printed circuit; asemiconductor layer comprising a first region and a second region, thefirst region constituting a channel formation region of the transistor;a first conductive layer on and in direct contact with the second regionof the semiconductor layer; a first inorganic insulating film over thefirst conductive layer; an organic insulating film over the firstinorganic insulating film and the first conductive layer; a secondinorganic insulating film over the organic insulating film and in afirst opening portion formed in the organic insulating film; and asecond conductive layer over the second inorganic insulating film, onand in direct contact with the first conductive layer in the firstopening portion formed in the organic insulating film, in a secondopening portion formed in the first inorganic insulating film, and in athird opening portion formed in the second inorganic insulating film,wherein the first opening portion, the second opening portion, and thethird opening portion each overlap a same portion of the substrate,wherein the first inorganic insulating film and the second inorganicinsulating film are in direct contact with each other in the secondopening portion formed in the organic insulating film, wherein, whenseen in a cross sectional view of the first opening portion, the secondopening portion, and the third opening portion, a side edge of the firstopening and a side edge of the third opening coincide, and wherein thesecond conductive layer is a pixel electrode of a pixel.
 15. The displaydevice according to claim 14, wherein the first inorganic insulatingfilm is on and in direct contact with the first conductive layer,wherein the organic insulating film is on and in direct contact with thefirst inorganic insulating film, wherein the second inorganic insulatingfilm is on and in direct contact with the organic insulating film, andwherein the second conductive layer is on and in direct contact with thesecond inorganic insulating film.
 16. The display device according toclaim 14, wherein, when seen in the cross sectional view, an entirety ofthe second opening portion and an entirety of the third opening portionoverlap with the first opening portion.
 17. The display device accordingto claim 14, wherein, when seen in the cross sectional view, a surfaceof the organic insulating film shaping an inner wall of the secondopening has a curvature radius continuously changed in the range of 3 μmto 30 μm.
 18. The display device according to claim 14, wherein theorganic insulating film is made from a positive type photosensitivefilm.
 19. The display device according to claim 14, wherein a surface ofthe organic insulating film shaping an inner wall of the second openinghas a continuously changed curvature radius, and wherein a contact angleformed by the surface of the organic insulating film in the secondopening with a bottom surface of the second opening is within a range of30° to 65°.